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Topic: Missing your target gravity... (Read 13665 times)

How can one deal with this on a brew day? If your pre-boil gravity is already too low, is there anything you can do to bump it up? I'm assuming this is a mash issue or a boil issue. Can a longer boil improve OG?

How can one deal with this on a brew day? If your pre-boil gravity is already too low, is there anything you can do to bump it up? I'm assuming this is a mash issue or a boil issue. Can a longer boil improve OG?

Yes, adding DME or boiling longer is an option.

Another option is to monitor the gravity in the mash. There is a relationship between the mash thickness and the gravity that the mash will have when all starches have been converted. By testing the gravity of the mash you can monitor how far along the mashing is and if you should mash longer or raise the temp of the mash for a mash-out/dextrinization rest. Here is some info: http://braukaiser.com/wiki/index.php/Troubleshooting_Brewhouse_Efficiency#Determining_Conversion_Efficiency (don’t be scared by the formulas. The table on the right is more important)

This assumes that your unexpected efficiency losses happened in the mash and not during lautering.

It also goes into the nomenclature used for efficiency. I like to be explicity and call the efficiency into the kettle “efficiency in the kettle”. Others call it mash efficiency some call it Brewhouse efficiency. The latter is also used to describe “efficiency into the fermenter” by some.

I deal with this issue from time to time as well. I usually just keep on going with my process and just understand that my beer will be off a little. I take good notes so that I can correct in the future. This is what I get hung up on: When your OG winds up lower than it should, this has a pretty large impact on the finished product. If you dont change your hopping schedule to compensate for the low OG, then your finished product is way off.

I like the idea of pulling more wort into the kettle and boiling it down to get your targeted OG but I guess I dont understand how to accurately accomplish this. You'd want to do the extra boiling at the front side instead of at the end of the boil as not to affect your hop utilization. So the question is, how do you know how long to boil or how much to boil off before you add your hops? Example:I brewed a Celebration Clone that was supposed to be 1.061. I always try to have 6 gallons in the kettle at the end of the brew day. About 2 qts get left behind and I transfer 5.5 G into the fermenter. After gravity readings and samples, I have 5 gallons to keg. So I pulled 8 gallons from my mash tun into my kettle and boiled for 90 minutes and wound up with 1.054. So I came up 5 points short. What is the process for determining how long or how much to boil off in order to hit my target OG before my hop additions? I dont want to be boiling my bittering hops for 90 minutes or 2 hours. Right?

You can try to estimate your boil off rate by taking refractometer readings throughout the boil. If you know what you started with on both the volume and SG side you can take the SG reading mid boil (or whenever) and determine approximately what your volume is at that point in time. From that, presuming you're boiling under constant conditions, you can estimate your boil off rate and determine how long you need to boil off to achieve your target gravity.

I usually don't worry too much about the 60 minute hops boiling for 90 minutes. The increased utilization doesn't seem that significant.

It's not 100% accurate but gives you an indication of where you are. I'm still working on tweaking it.

Wouldn't it work to not start timing your boil until you reached your 8 gal starting mark? You pull off an extra gal so you have 9 gal into the kettle. Start boiling and when you have boiled off the extra gal, and are down to 8 gal in your kettle, then start your time and do you hop additions as normal.

I don't know if that would get you to the correct gravity, but it would allow you to time the hop additions and have the same volumes you mentioned in you example

I have seen heated discussions over what exactly Brewhouse efficiency is. Some asses it in the kettle and others in the fermenter. And since even the literature is not clear on this I like to stay away from this ambiguous term and be more explicit. I also don't like that Mash Efficiency is used to describe efficiency into the kettle. But because of that I call the efficiency of the mash conversion efficiency.

Regarding boiling longer:

I don’t particularly like the idea of making up for low efficiency into the kettle by sparging more. There is only so much more you can get out of the grain before you end up sparging too much. This and the extended boil time may also have a taste impact on the beer. Adding DME is a better option, but requires you to have DME at hand. And that’s something that many AG brewers don’t want to stock.

Each point*gallon you are missing in the kettle equals about 10g DME. If you are missing 5 points and have 6 gallon you need to add 300g DME. ( I hope this math is correct)

When I had erratic efficiencies I used to aim low with the efficiency and would freeze use any surplus wort for future use as starters or for priming beer. My logbook pages still have a field for post boil dilution water to correct the gravity but I haven’t done that in a long time.

I don’t particularly like the idea of making up for low efficiency into the kettle by sparging more. There is only so much more you can get out of the grain before you end up sparging too much. This and the extended boil time may also have a taste impact on the beer. Adding DME is a better option, but requires you to have DME at hand. And that’s something that many AG brewers don’t want to stock.

This really depends on the beer. Not a bad rule Kai, but for especially big beers where (and I do) am pulling 1.040 when I stop my sparge it is not a problem, but. . .

as Kai said continuing to sparge and boil longer will have a flavor impact. If you are sparging past the limit 1.010, 1.008 if I recall correctly you could start to pull astringency out of the mash.

You could as easily add good old table sugar, that is something most people have in their pantry. Or a combination of longer boil and sugar, since their effects to some extent offset each other (one drier, one less).

I'm 5 batches into all grain brewing and this was a major problem for me. I just read Designing Great Beers by Ray Daniels and in it he lays out a method for calculating final gravity using the total gravity points. You do need to know the volume in the kettle to do the calculations. Basically you figure out your total gravity points for your target gravity and compare them to the total gravity points in the kettle.

So if you have a target gravity of 1.050 you take the gravity points, 50, and multiply it by your final volume of 5 gallons for 250 total gravity points.

Now after your mash take a gravity sample (make sure to correct the reading for temp or stick the sample in the fridge to cool off). Lets say you have 6.5 gallons in the kettle with a gravity of 1.040. The total gravity points would be 40 X 6.5 which equals 260 total points.

If you divide the total points in the kettle by your target volume you can calculate your final gravity: 260/5 = 52 or 1.052.

If you are below your target add malt extract based on gravity points per gallon...sorry I don't have the numbers handy but Kai gives a number in a previous post...